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Certainly, Jack. The shunt needs to be in a line close to the controller ground, and the common mode rejection of the instrumentation amp has to handle whatever difference there is. Even large common mode voltages can be accommodated with transformer coupled guard shielded amps. If we can place the shunt in a part of the circuit that isn't switched (I guess that is the B+ line, and the conjterol board ground is at or near the B minus, right?) Would the shunt in the B minus lead give us the info we need for feedback? If so, the common mode voltage would be only a volt or so, being voltage drops in the busbar and cables. So the AD623 for example, which runs on +12 single supply and tolerates common mode as much as 150 mV below the negative supply, should handle getting the shunt voltage up to what the Hall ckt was giving.
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